1. Field of the Invention
The present invention relates to an actuator having a movable plate allowed to move, and more particularly, it relates to an actuator that displaces a movable plate in directions horizontal to a flat surface the movable plate.
2. Description of the Related Art
Jpn. Pat. Appln. KOKOKU Publication No. 1-35550 discloses a video camera aiming at an increase in resolution of an image by utilizing a piezoelectric actuator. A structure of this video camera will now be described hereinafter with reference to FIG. 11.
As shown in FIG. 11, a solid-state image sensing device chip substrate 610 is supported by two bimorph piezoelectric elements 611A and 611B fixed to a support base 612. Here, the solid-state image sensing device chip substrate 610, the bimorph piezoelectric elements 611A and 611B and the support base 612 constitute a piezoelectric actuator that displaces the solid-state image sensing device chip substrate 610 in directions horizontal to a flat surface of the chip substrate 610.
A light input is transmitted through an imaging lens 613 and image-formed on the solid-state image sensing device chip substrate 610. The bimorph piezoelectric elements 611A and 611B displace the solid-state image sensing device chip substrate 610 in directions vertical to an optical axis with a resonance frequency corresponding to a frame cycle upon receiving vibration pulses generated by a pulse driver 614, a tr, tf control circuit 615 and a trapezoidal wave generation circuit 616.
A timing generation circuit 617 generates necessary synchronization pulses such as a timing signal of a PH/2 delay circuit 618 required to delay a timing of a horizontal read register by a quantity corresponding to ½ of a horizontal pixel pitch PH, a timing signal of a vertical register and others. The solid-state image sensing device chip substrate 610 is driven by a clock driver 619, and an output signal obtained from the solid-state image sensing device chip substrate 610 is processed into a predetermined signal waveform through a preamplifier 620 and a process amplifier 621. A signal reproduction circuit 622 performs processing matching with a spatial sampling point based on first vibration and outputs a result.
Since a reproduced image on a monitor is displayed by adding a field A and a field B, a resolution in the horizontal direction is improved to be two times. That is, the video camera shown in FIG. 11 realizes an increase in resolution of an image by moving the imaging element in directions orthogonal to the optical axis by using the piezoelectric actuator.
The piezoelectric actuator according to the prior art utilizes a piezoelectric material. Therefore, a relationship between a drive signal (applied voltage) and a displacement quantity has hysteresis characteristics.
Further, in the video camera shown in FIG. 11, the bimorph piezoelectric elements 611A and 611B are repeatedly displaced in directions vertical to their flat surfaces in a cycle of 1/30 second or 1/60 second which is a period corresponding to ½ of one frame cycle or ½ of one field cycle. Therefore, there is a possibility that sound waves at a lower frequency involved by that displacement, i.e., vibration sounds may be generated. Since such vibration sounds become noises when recording sounds, it is desired that generation of such vibration sounds is as small as possible in an application of the video camera.